Modelling a Novel Superoxide Dismutase 1 Mutation in Motor Neurons: An Insight into Molecular Pathomechanism of Amyotrophic Lateral Sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal, adult onset neurological disorder characterized by progressive degeneration of upper and lower motor neurons. ALS is a multifactorial disease with a complex etiology and misfolded protein aggregates are considered as the major neuropathological hallmark. Several genetic mutations are associated with familial and sporadic forms of ALS. We have recently reported the first mutation in Superoxide Dismutase 1 (SOD1) in a family with ALS from India. The purpose of this study is to explore the functional consequences of L84F SOD1 mutation using in‐vitro cell model. We observed that this novel triallelic mutation (L84F) caused metal chelation and destabilized the native SOD1 dimer. Cells expressing mutant SOD1 showed increased protein carbonylation and were more sensitive to oxidative stress. Further, L84F SOD1 mutant readily formed detergent‐resistant aggregates in motor neuronal cell line. Modulating protein homeostasis pathways led to enhanced aggregation of mutant SOD1. Interestingly, the cells expressing mutant SOD1 exhibited significant decrease in neuronal differentiation compared to wild type. Our data shows that altered differentiation in mutant SOD1 cells is probably due to hampered autophagy and aberrant deposition of misfolded protein. We also observed that treatment with flavonoids including curcumin, luteolin abolished mutant SOD1 aggregates by inducing autophagy.ALS pathology also involves disassembly of neuromuscular junction (NMJ) which leads to muscle atrophy. However, the series of events that leads to skeletal muscle denervation is poorly understood. To examine the effect of mutant SOD1 on NMJ, we have established an in‐vitro NMJ model by co‐culturing skeletal muscle and motor neuronal cells. We are currently using this model to delineate the neuron‐ and muscle‐ specific cues that affects the structural and functional integrity of NMJ. To conclude, L84F SOD1 mutant exhibits characteristics of ALS such as aggregation of misfolded protein and deregulated proteasome machinery. Further targeting protein homeostasis pathways may aid in developing novel therapeutics for ALS.Support or Funding InformationAuthors acknowledge Indian Council of Medical Research (ICMR) (Project Code: 1.3.2.183.025) and Research Development Program (RDP) at Sir Ganga Ram Hospital for funding the research project. SV acknowledges Council of Scientific and Industrial Research (CSIR) and AV, SK acknowledges Indian Council of Medical Research (ICMR) for fellowships.